Brian Skerry knows the ocean well.
A diver for thirty years, and a photographer for 28, he's spent decades documenting the magnificence of the sea and its creatures.
But over as the years, as man perfected the hunt for fish and pollution poisoned the world's waters, he began to notice a major decline in the wildlife that once flourished in the sea. His concerns were confirmed by science when he read a study showing 90 percent of the big fish in the ocean were gone.
"I was just blown away by that statistic," said Skerry, who spearheaded a three-year effort to capture the global fisheries crisis, featured in the April edition of National Geographic. "I felt that it wasn't on anybody's radar. So I proposed a story on overfishing, but from an underwater perspective."
Skerry's journey to chronicle the unseen world of the sea took him around the globe, as he searched for the reasons why fish were disappearing and what could be done to bring them back.
What he found was sobering.
"The oceans are in real trouble right now," Skerry said. "I think they suffer from a lot of problems, but overfishing is one of the biggest that's occurring right now. And it's a problem we can fix."
Nearly one billion people around the world, mainly poor, rely on fish as their only source of protein. A 2004 U.N. assessment says nearly a third of the world's fish stocks are overfished. As this resource diminishes, these people will have to find another way to eat.
For Skerry, the Bluefin tuna is a metaphor for what's happening in the sea.
"We just keep wiping them out and moving down the food chain, but pretty soon, there won't be anything left," said Skerry, who's been photographing these animals for years. "But there's such a demand for sushi, and there's such a bounty on these animals' heads, that it's almost impossible to protect them."
One of the world's most magnificent fish, the Bluefin tuna can criss-cross entire oceans and swim from the Arctic to the equator. They measure up to 12 feet in length, and can live for 30 years. But people have become so efficient at harvesting these fish that they face an uncertain future.
"I wanted to show people the animals that we were losing, the magnificent animals that are the lions and tigers of the sea perhaps," he said. "And also to show the destructive methods that are often used to catch these animals, to harvest them. Methods that would never be tolerated on land."
Skerry went to Spain to document their recent plight, where high tech fishing techniques and wasteful management have brought their numbers to dangerous lows, he said.
"People have to understand that we're losing a precious resource that not long ago there were millions of Bluefin tuna swimming through our oceans, and today there are only a few left," he said.
Perhaps because fish are so hidden under the depths of the sea that people on land don't understand what they're losing, Skerry said.
"The ocean suffers from things that would never be tolerated on the land, largely because we don't see what's going on," he said.
Current fishing practices throughout the world have had a devastating impact on fish wildlife. Lack of international regulation and sustainable management create additional hurtles.
But in his photographic sojourn, Skerry discovered some solutions.